GB2190020A - Magnetic recording medium - Google Patents

Description

GB 2 190 020 A 1 SPECIFICATION roughness thereof, and that a magnetic

recording medium obtainedby usingthisfilm asthe base Magnefir, recording medium material exhibits a good electromagnetic converting property and stabletravelling property,wear resist-

BACKGROUND OFTHE INVENTION ance and scuff resistance without a back coat layer.

The present invention relates to a magnetic record- The present invention has been achieved on the basis ing medium which comprises a biaxially oriented of these findings.

polyesterfilm having an extremely lowsurface SUMMARY OF THE INVENTION roughness and a magnetic layerformed on one side 70 In thefirst aspect of the invention,there is provided thereof, and which exhibits a high quality, a high a magnetic recording medium comprising a biaxially density and an excellent travel ling property even. oriented polyesterfilm showing the average surface when it is not provided with a back coat layer. roughness Ra of 0.005to 0. 013 pm, the static More particularly, the present invention relatesto a coefficient (I1s) of film-film friction of not more than magnetic recording medium comprising a biaxially 75 0.28,the dynamic cofficient (PMd) of film-film friction oriented polyesterfilm which contains veryfine of not morethan 0.28, and the maximum coefficient particles and specific higher aliphatic carboxylicacids of friction of not morethan 0.30 during 50-time andlor derivatives thereof, and which exhibitsspecl- repeated travelling, said biaxially oriented polyester fie average surface roughness, coefficient of friction film containing, with respectto 100 parts byweight of and coefficient& friction during repeated travellings, 80 Polyester.

and a magnetic layerformed on one side of the (A) 0.001 to 1.0 part byweight of inner particles polyester film. The magnetic recording medium having an average diameter of 0.1 to 1.5 pm and/or according to the present invention is excellent in inactive additional particles having an average dia electromagnetic characteristics, travelling property, meter of 0.1 to 1.0 pm and wear resistance and scuff resistanceeven if itis not 85 (B) 0.005to 2 parts byweightof an organic lubricant provided with aback coat layer, and can be produced which comprises a mixture of higher aliphatic mono at a low cost. carboxylic acids having respectively different carbon High-quality and high-density magnetic recording numbers of not less than 18 andlor a mixture of media, above all, video tapes have recently been derivatives thereof having respectively different car increasingly developed. Specifically, as 112-inch go bon numbers of not lessthan 18, contains not less video tapesfor home use,tapes having a high SIN than 10 wt% of higheraliphatic monocarboxylic ratio which are called a super high grade or extra high acid(s) having not lessthan 34carbon atoms andlor gradetypetapes have been chiefly used. In thistype derivative(s) thereof having not lessthan 34 carbon of videotapes, a film having an extremely small atoms, and has a melting point of 80to 20WC, surface roughness is used asthe basefilm in orderto 95 said higheraliphatic monocarboxylic acids and enhancethe S/N ratio, and a backcoat layer is derivatives thereof being represented byformula (l):

generally provided onthe opposite side of the R 12 magneticlayer, because stable travelling cannotbe R 1 - C - COOR, maintained by merely providing a magnetic layer on 3 the base film.

However, formation of both of a magnetic layer and wherein R, represents an alkyl group or an unsatu a back coat layer on the sides of a base film in the rated hydrocarbon group having not less than 10 process of producing a magnetic tape requires an carbon atoms, R2 represents an alkyl group having extra equipment and complicated steps which may 100 not less than one carbon atom or an unsaturated lowerthe yield, resulting in a rise in the cost. hydrocarbon group having not less than 2 carbon Therefore, development of a magnetic recording atoms, R3 represents a hydrogen atom, an alkyl group medium has been strongly demanded, which has a having not lessthan one carbon atom, or an basefilm having an extremely low surface roughness unsaturated hydrocarbon group having not lessthan and is provided with fundamental properties of a 105 2 carbon atoms, and R4 represents a hydrogen atom, magnetictape such as stable travelling property, a metal, an alkyl group having not lessthan one scuff resistance, prevention of producing white carbon atom or an unsaturated hydrocarbon group powder, etc. during thetravel without a backcoat having not lessthan two carbon atoms,the total layer. number of carbon atoms in R,, R2, R3 and R4 being not As a result of researches to provide a magnetic 110 lessthan 16; and recording mediurnwhich exhibits the above-de- a magnetic layer provided on one side of said scribed excellent properties without a backcoat layer, polyesterfilm the present inventors havefound that a biaxially In the second aspect of the invention,there is oriented polyesterfilm which contains veryfine provided a processfor producing a magnetic record particles and specific higher aliphatic carboxylic acids 115 ing medium comprising the steps of andlor derivatives thereof, and is obtained by an mixing a polyester polymer containing 0.001 to 1.0 6o. appropriate method, if necessary, can improvethe part byweight of inner particles having average s[ipping property. in spite& an extremely low surface diameter of 0.1 to 1.5 lim and/or inactive additional This printtakes account of replacement documents submitted afterthe date of filing to enablethe application to comply with the formal requirements of the Patents Rules 1982.

GB 2 190 020 A 2 particles having an average diameterof 0.1 to 1.0 lim (A) 0.001 to 1.0 part byweightof inner particles with respectto 100 parts by weight of polyester, with having an average diameter of 0.1 to 1.5 pm andlor 0.005to 2 parts by weight, with respectto 100 parts by inactive additional particles having an average dia weight of polyester, an organic lubricantwhich 65 meter of 0.1 to 1.0 pm and comprises a mixture of higher aliphatic monocar- (B) 0.005to 2 parts by weight of an organic boxylic acids having respectively different carbon lubricant which comprises a mixture of higher numbers of not less than 18 andlor a mixture of aliphatic monocarboxylic acids having respectively derivatives thereof having respectively different car- different carbon numbers of not less than 18 andlor a bon numbers of not less than 18, contains not less 70 mixture of derivatives thereof having respectively than 10 wt% of higher aliphatic monocarboxylic different carbon numbers of not less than 18, acid(s) having not less than 34 carbon atoms andlor contains not less than 10 wt% of higher aliphatic derivative(s) thereof having not less than 34 carbon monocarboxylic acid(s) having not less than 34 atoms and has a melting point of 80 to 200'C, said carbon atoms andfor derivative(s) thereof having not higher aliphatic monocarboxylic acids and derivaless than 34 carbon atoms, and has a melting point of tivesthereof being represented byformula (l): 80 to 2001C, R said hig her al iphaic monoca rboxyl ic acids and de l 2 rivatives thereof being represented byformula (l):

1 - C - COOR4 (1) 1 3 R 12 wherein R, represents an alkyl group oran unsatu- R1 C - COOR4 (1) rated hydrocarbon group having notlessthan 10. 3 carbon atoms, R2 represents an alkyl group having wherein R, represents an alkyl group oran unsatu not lessthan one carbon atom or an unsaturated 80 rated hydrocarbon group having not lessthan 10 hydrocarbon group having not lessthan 2 carbon carbon atoms, R2 represents an alkyl group having atoms, R3 represents a hydrogen atom, an alkyl group not lessthan one carbon atom or an unsaturated having not iessthan one carbon atom, or an hydrocarbon group having not lessthan 2 carbon unsaturated hydrocarbon group having not lessthan atoms, R3 represents a hydrogen atom, an alkyl group 2 carbon atoms, and R4 represents a hydrogen atom, 85 having not less than one carbon atom, or an a metal, an alkyl group having not less than one unsaturated hydrocarbon group having not less than carbon atom oran unsaturated hydrocarbon group 2carbon atoms, and R4represents a hydrogen atom, having notlessthan two carbon atoms,thetotal a metal, an alkyl group having notlessthan one number of carbon atoms in R,, R2, R3 and R4 being not carbon atom or an unsaturated hydrocarbon group lessthan 16; 90 having not lessthan two carbon atoms,thetotal melt extruding the mixture at a temperature of 250 numberof carbon atomsin R,, R2, R3and R4being not to310'Cinto an amorphousfilm; lessthan 16; and stretchingthe amorphousfilm inthe machine a magnetic layer provided on one side of said direction by 2.0 to 8.0 times at a temperature of 75 to polyesterfilm.

14WC so thatthe double refractive index after 95 "Polyester" used in the present invention mainly stretching is 0.030to 0.130; means polyethylene terephthalate and polyethylene stretching the thus obtained film in the transverse 2,6-naphthalate. Polyester in the present invention direction by 2.0 to 5.0 times at a temperature of 90 to further includes polybutyleneterephthalate, poly 150,C; butylene dibenzoate, polyesters obtained from bis- heat setting thethus biaxially stretched film at a 100 phenol A and a terephthalic acid or an isophthalic temperature of 200 to 2400Cfor 1 to 60 seconds, acid, and polyesters obtained by copolymerization of thereby obtaining a biaxially oriented polyesterfilm each monomer of the above-described polyesters showing the average surface roughness Ra of 0.005 and ethylene glycol, propylene glycol, butanediol, to 0.013 11m, the static coefficientf riction (g,,) of xylene glycol, bisphenol A, diethylene glycol, film-film of not morethan 0.28,the dynamic coeffi- 105 polyethylene glycol, polytetra methyl e ne glycol, cientfriction (I1d) Offilrn-filM of not morethan 0.28, polypropylene glycol, adipic acid, sebatic acid, phtha and the maximum coefficient friction of not more lic acid, isophthalic acid, 2,6-naphthalene dicarboxy than 0.30 during 50-time repeated travelling; and lic acid, p-oxyethoxy benzoic acid, glycolicacid, etc. It forming a magnetic layer on one side of said also includes p:flypropyleneterephthalate, biaxially oriented polyesterfilm. 110 polypentylene bibenzoate, a polyester of 3,3 - bis(p DETAILED DESCRIPTION OF THE INVENTION oxyphenyi)pentane and terephthalic acid, a polyester

The present invention provides a magnetic record- of 2,2 - bis(3methyloxyphenyl)propane and tereph ing medium comprising thalic acid, a polyester of 2,2 - bis(p - oxyphenyl)pen a biaxially oriented polyesterfilm showing the 115 tane and isophthalic acid orterephthalic acid, a average surface roughness Ra of 0.005 to 0.013 pm, copolymerized polyester of ethylene terephthalate or the static cofficient (ps) of film-film friction of not ethylene isophthalate, and a copolymerized polyes morethan 0.28,the dynamic coefficient (I1d) of ter obtained by using sebacate, adipate, 1,4- cyc film-film friction of not morethan 0.28, and the lohexanedimethanol, etc. as a copolymerization com maximum coefficient of friction of not morethan 0.30 ponent. The polyester in the present invention is, of during 50-time repeated travelling, said biaxially 120 course, not restricted to the above-described exam oriented polyesterfilm containing, with respect to ples.

parts by weight of polyester, The inner particles used in the present invention 3 G B 2 190 020 A 3 are particles produced from at least one compound 70 From this viewpoint, titanium oxide, synthetic cal which are generally added atthe time of synthesis of cium carbonate, zeoiite, silica, etc. are preferable as a polyester, such as a calcium compound, a magne- the small particles. As the large particles, calcium sium compound and a lithium compound and a carbonate, calcium oxalate, lithium fluoride and, monomer or an oligomerwhich constitues a polyes- among all, calcium carbonate is preferable.

ter. The inner particles used in the present invention 75 If the contentof the innerparticies andlor inactive may contain a phosphorus element and/or other additional particles is lessthan 0.001 part by weight metal components, for example, zinc, cobalt, anti- with respectto 100 parts byweight of polyester, the mony, germanium and titanium in a range in which coefficient of film-film and film - metal friction the effects of the present invention are not impaired. becomes large, and the slipping property is impaired.

The average particle diameter of the inner particles is 80 On the other hand, if the content exceeds 1 part by 0.1 to 1.5 lim. weightwith respectto 100 parts byweight of The inactive additional particles used in the present polyester, many coarse particles are produced and invention arejorexample, inorganic salts, oxides or the surface roughness increases, thereby disadvan organic salts of the elements of groups 1, 11, Ill and W in tageously impairing theflatness of the surface of the the periodictable and are chemically inactive. They 85 polyesterfilm.

are exemplified by kaolin, talk, magnesium carbon- The higher aliphatic monocarboxylic acids and ate, calcium carbonate, barium carbonate, calcium derivatives thereof, both having not less than 18 sulfate, barium sulfate, lithium phosphate, calcium carbon atoms used in the present invention as an phosphate, magnesium phosphate, aluminum oxide, organic lubricant are represented bythefollowing silicon oxide, titanium oxide, lithium fluoride, Ca, Ba, 90 formula (l):

Zn and Mn salts or oxalic acid and terephthalic acid, R and the particles of carbon blacks. The inactive l 2 additional particles are also not restricted to the R1 C - COOR4 above examples. The inactive additional particles R3 may be spherical, bulky, orflaky, and there is no wherein R, represents an alkyl group or an unsatu special restriction in the hardness, specific gravity rated hydrocarbon group having not lessthan 10, color orthe like. The average particle diameter of the preferably 16 - 44 carbon atoms, R2 represents an inactive additional particles is 0. 1 to 1.0 pm, prefer- alkyl group having not less than one, preferably 1 - 3 ably 0.3 to 1.0 lim. If it is smallerthan 0.1 I.Lm, the 95 carbon atoms or an unsaturated hydrocarbon group slipping property of the polyesterfilm is insufficient, having not less than 2, preferably 2 - 3 carbon atoms, while if it exceeds 1.0 pm, the flatness of the polyester R3 represents a hydrogen atom, an alkyl group having film is impaired. not less than one, preferably 1 - 3 carbon atoms, or Coarse particles are removed from the inactive an unsaturated hydrocarbon group having not less additional particlesto adjustthe particle size by 100 than 2, preferably 2 - 3 carbon atoms, and R4 various known grinding and/or classifying methods represents a hydrogen atom, a metal, an alkyl group such as air classification, natural sedimentation or having not lessthan one, preferably 1 - 17 carbon centrifugal sedimentation performed after making atoms or an unsaturated hydrocarbon group having the particles into an ethylene glycol slurry or a water not lessthan two, preferably 2 - 17 carbon atoms,the slurry, and grinding by a sand mill. 105 total numberof carbon atoms in R, , R2, R3 and R4 A polyesterfilm according to the present invention being not lessthan 16, preferably 32 - 50.

must contain at leastone of the inner particles and the As a metal for R4, an alkaline metal or an alkaline inactive additional particles. The amount of the earth metal such as lithium, sodium, potassium, particles is 0.001 to 1 part byweight, preferably 0.01 barium, magnesium, calcium and strontium is used.

to 0.5 part byweightwith respectto 100 parts by 110 Above all, sodium is preferable from the point of view weight of polyester in both the case where the of the thermal stability of the polyester.

polyesterfilm contains only one of the inner particles If the higher aliphatic monocarboxylic acid having and the inactive additional particles or both particles. less than 18 carbon atoms is used, the bleedout It is preferable that 0.1 to 1.0 part byweight of small thereof to the su rface of the polyesterfilm impairs the particles having an average particle diameter of 0.1 to 115 adhesion between the magnetic layer and the polyes0.6 lim and 0 to 0. 1 part by weight of large particles terfilm. In orderto preventthe bleedout and enhance having an average diameter of 0.4to 1.0 lim are the adhesion between the magnetic layer and the contained with respectto 100 parts byweight of polyesterfilm, it is preferablethat not less than 10 polyester. Although the inner particles may be used wt% preferably, not less than 20 wt% of higher as the small particles while using the inactive additional particles as the largeparticies, it is 120 alipaticmonocarboxylicacid(s)andlorderivative(s) thereof, both having not less than 34 carbon atoms preferable that both the small particles and the large are contained in the organic lubricant. It is more particles are the additional particles. In the present preferable thatthe organic lubricant used in the invention, the slipping property set forth below present invention substantially consist of higher contribute mainlyin lowering the coefficient of 125 al i phatic monocarboxyl ic acid (s) andlorderivative(s) friction of a polyesterfilm, butthe shapes of the thereof both having not less than 34carbon atoms.

particles, distribution of the particles in the polyester The melting point of the organic lubricant is 80to film and the particle diameter of the particles are also 20WC, preferably 1 00to 20M.

the important factors which affectthe coefficient if the melting point is under80'C, thethermal friction afterthe film is made into a magnetictape. 130 stability of the polyester is disadvantageously im- GB 2 190 020 A 4 paired. Ontheother hand, ifthe melting point is more exceedsO.28, itis impossibleto obtain a stable than 20WC,the dispersion thereof intothe polyester travelling property without a backcoatlayer.

is insufficient, thereby unfavorably impairing the Itisalso necessary thatthe maximum coefficient& flatness of the surface of the polyester film. friction ofthepolyesterfilm accordingtothe present The content of the organic lubricant is 0.005 to 2 70 invention during 50- time repeated travel lings is not parts byweight, preferablyO.01 to 1 partbyweight, morethan 0.30. If itexceedsO.30, itisdifficuitto use a and more preferably 0.05to 0.5 part by weight with magnetic recording medium having such polyester respectto 100 parts byweight of polyester. If the film as the base repeatedly.

content is lessthan 0.005 parts byweight,the slipping The polyesterfilm according tothe present inven- property is notsufficient, while if itexceeds 2 parts by 75 tion is a biaxially oriented film. If it is not a biaxially weight,the bleedoutthereof to the surface of thefilm oriented film, it is difficuitto obtain the polyesterfilm occurs unfavorablyso much asto greatly reducethe having the surface roughness and the coefficient adhesion between the magnetic layerand the polyes- friction in the abovedescribed ranges, and the terfilm. uniformity in thickness,the rigidity and the dimen- The higher aliphatic monocarboxylic acid(s) and 80 sional stability of the polyesterfilm are unsuitably derivative(s) thereof (salts and esters) may be used impaired.

alone or in combination. The sufficient resuitforthe Biaxial orientation is carried out in a known object of the present invention is obtained by using method, and it is preferable that biaxial orientation is the higher aliphatic monocarboxylic acid(s) or deriva- carried out so that the average refractive index (R), tive(s) thereof alone. Therefore, in the case of 85 the degree of surface orientation (A p) and the double combination use,the higher aliphafic monocarboxy- ref ractive index (A n) of the biaxially oriented film lic acid(s) and derivative(s) thereof may be mixed in satisfythe following relationships (2), (3) and (4), any ratio. respectively, by limiting the double refractive index In orderto enhance the slipping property of the afterstretching in the machine direction to a low poiyesterfilm, which is the basefor a magnetic 90 value or relaxing the stretched film in the transverse recording material, natural higher aliphatic monocar- direction atthe time of heat setting, thereby impro boxylic acids and metal salts or esters thereof have ving the travelling property, thewear resistance and been used (Japanese Patent Application Laying- the scuff resistance.

Open (KOKAI) Nos. 59-221354 (1984) and 60-82326 1.600-' 1.606... (2) (1985)).However,those natural compoundsare 95 A p -5 1.43 5 - 2.128... (3) expensive and have a constant number of ca rbon A n:- 20 X 10-3... (4) atoms. Furthermore, no natural higher aliphatic In the film which shows the physical values monocarboxylic acid having 34 or more carbon satisfying the above- mentioned relationship, it is also atoms is known. In contrast, in the case of the preferable thatthe number (A) of pair of protuber synthetic higher aliphatic monocarboxylic acid(s) 100 ances and depression, which is derived from the and derivative(s) thereof used in the present inven- protuberances and has a major axis of at least 2 pm, tion, it is possible to synthesizethose having not less perone MM2 of the surface of the film satisfies the than 34 carbon atoms. The slipping property of the following relationship (5).

polyesterfilm can beenhanced by using a small 5:g (5) amountof the organic lubricantwhich contains not 105 Ithas been confirmed thatthe travelling property of lessthan lOwt%, preferably not lessthan 20 wt%, the polyesterfilm according to the present invention and more preferably almost 100% of higher aliphatic depends upon the intrinsic viscosity of the polyester, monocarboxylic acid(s) andlorderivative(s) thereof and the intrinsic viscosity [nh of thefilm is not more having not lessthan 34carbon atoms. It is preferable than 0.65, preferably not morethan 0.62, and more thatthe contentof higher allphatic monocarboxylic 110 preferably not morethan 0.60.

acid(s) andlor derivative(s) thereof having not less A polyesterfilm having the above-described char than 50 carbon atoms is less than 3%. If it is 3% or acteristics is produced by a known method, for more, theflatness of the surface of the polyesterfilm example, in the following way.

is unfavourably impaired. High aliphatic carboxylic acid(s) andlor deriva The average surface roughness (Ra) of the polyes- 115 tive(s) thereof are dry blended with a polyester terfilm according to the present invention, measured containing a predetermined amount of inner particles by a method setforth later, is 0.005 to 0.013 lim, andlor inactive additional particles by means of an preferably 0.008 to 0.013 lim, and more preferably extruder orthe like. The thus-obtained master batch 0.008to 0.011 gm. If the average surface roughness is mixed with a polyester andlor another master (Ra) is less than 0.005 lim, the polyesterfilm is too flat 120 batch, if necessary, and the mixture is dried by an to show a stable travelling property without a back ordinary method, melt extruded at a temperature of coat layer. On the other hand, if Ra exceeds 0.013 pm, 250 to 31 WC, and rapidly cooled by an electrostatic the flatness is too lowto be used as a super high contact method or the like, therebyforming an grade or extra high grade magnetic recording amorphousfilm.

medium. 125 The amorphous film is stretched in the machine The static and dynamic coefficients of film -film direction by2.Oto 8. Otimesat75to 140'Csothatthe friction of the polyesterfilm in the present invention, double refractive index is 0.030to 0.130. The stretch measured by a method set forth later, are not more ed film is then further stretched in the transverse than 0.28, preferably 0.1 5to 0.25. If eitherthe static direction by 2.0 to 5.0 times at 90to 150'C, and coefficient friction or dynamic coefficient friction 130 therefore is heatsetat200to240'Cfor 1 to 60 seconds GB 2 190,020 A 5 to obtain a biaxially,orientedfilm. It is preferablethat polyesterfilm, the polyesterfilm was subjectedto the biaxially stretched film is subjectedto relaxation travelling ata rate of 1 mlsec, and resistanceT, of the in thetransverse direction by Oto 10% atthetime of other end was measured. The dynamic coefficient heatsetfing. friction was obtained from thefollowing formula.

So long asthe average refractlive index (-a),the degree of surface orientation (Lp) andthe double 1 T1 refractive index (An) of the polyesterflim satisfythe in!F2 relationships (2),(3) and (4), respectively, the film maybe restretched inthemachine and/orthe 70 During 50-time reciprocating travellings, IldfOr transverse directlion, re-heat-set or subjected to eachtimewas obtained andthe maxumum Pclwas r'laxaf determined as [Inax.

e ion inthetransverse direction atthetime of heatsetting. (4) Evaluation of wear resistance A magnefic recording medium according to the A polyesterfilm which had been slitto a width of 1.0 present invention is obtained by providing a magne- 75 mm was subjected to travelling over a length of 200 fic layer onone side ofthethus-obtained biaxially m, and the amountof abrasion dustwhich had oriented film. The magnetic layer is formed by adhered to a fixed pin,(6 mm in diameter, finished dispersinga powdery magnetic material such as viCith hard chromium plating) was visually evaluated y-Fe203,V-Fe203dopedmfith Co,Cr02oraferro- on the basis of thefollowing criteria. Thetravelling magneticalloyin an organic binder, applying the 80 speed of the polyesterfilm was 10 m/min,the initial dispersionto oneside of the blaxially oriented tension was 300 gr,,and the angle of contactofthe polyesterfilm, magneficallyoCientafing and polyesterfilmtothe pinwas 135% clenderi a ing, according tothe conventional method. No adhesion of abrasion dust A magnefic recording medium accordinglothe 0 Hardlyany adhesion of abrasion dust present inventlio n obtained in this manner has a 85 L Slight adhesion of abrasion dust polyesterfil m of Sto 27 pm, preferably 9to 25 lim x Muchamountofadheslon of abrasion dust thick, and a mag nefic layer of 1 to 10 pm, preferably 2 Evaluation ofthe adhesive strength between a to 8 pm thick, and it exhibits such excel] ent electro- magneticlayer.and. apolyesterfilm magnetic characte fistl cs, stab] etravel ling p roperty, A double-sided adhesivetapewas applied on a wear resistance and scuff resistanceasto berequired go stainless steel sheet of 1 mmt'hick,andthe magnetic fora high-quality and high-densityrnagneficrecord- layerof a video type was applied onthe otherside of ing medium vCithouta backcoat layer- Since the steps the adhesive tape. The polyester base film was then forforminga backcoatlayeris unnecessary, itcan be peeled offthemagnetic layeratan angle of 180% and produced industrially advantageously. the resistance atthattime was measured by means of The present invention will be explained in more 95 Tensfi on. The peeling speedwas 1 m/min and the detail while referring tothefollowing non-limitative a dh es ive strength was represented by a relative ratio examples. with respectto a referencetape.

The evaluation ofthe characteristlics of a polyester (6) Travellingproperty and scuff resistance of a film and a magnetic recording medium according to magnetictape the present invention was made in the following 100 A magnetic recording tapes recorded with signals manner. of 7,000 Hzwas mounted on a video tape recorder (1) Average surface roughness Ra and was subjected to travelling at a speed of 10 The surface roughnesswas obtained bythe cm/sec, while repeat] rig the starting and stopping method descriffied in JIS B0601-1976 by using a operations. Thetest was continued until the travell surface roughness measuring machine model SE-317 105 ing time reached 100 hou rs, while measuring the produced by Kosaka Kenkyusho, Ltd. The radius of power output. Among the tapes which hadtravelled thefip ofthe contact needlewas2 pm, andthe load smoothly without entangling tothe guide rollers was30 mg,the cut-off valuewas 0.08 mm, andthe during thattl me, tapes with the drop in poweroutputs measuring lengthwas2.5 mm.Thesurface rough- of lessthan 1.0dBwerejudgedto have a-verygood nesswasmeasured at 12points, andan average of 110 travelling property", those with th e drop in power measurements atl 0 pointswas obtainedwiththe outputs lessthan2.0 dB werejudgedto have a "good maximum and minimumvalues rembved. travelling property", and those with the drop in (2) Static and dynamic coefficients offilm -film power outputs of 2.0 dB or morewere judged to have friction a---badtravelling property". The film surface after The coefficients of film -film friction were mea- 115 100-hourtravelling was observed bya microscope, sured in accordance with ASTM-D-1 8941363 by using and the scuff resistance was evaluated on the basis of a slip tester. thefollowing criteria.

(3) The maximum coefficient offriction during 1 Hardlyanyscuff repeated travelling 2 Intermediate The maximum coefficient of friction was measured 120 3 Fullofscuffs bythe method described in Japanese PatentApplica- (7) Electromagnetic converting property tion Laying-Open (KOKAI) No. 61-47235 (1986). A When a magnefic recording medium was subjected polyesterfilm which has been slitto a narrowwidth to playback,the medium showling a strong output wassubjectedto contacting with afixed metal roll signal and a flatslignal wavewasjudgedto be plated with hard chromium at an angle of 135'(0). 125 "good", whilethe medium showing aweak output Whileapplying a load of 53g (T2) to one end ofthe signal or a deformed signal wave was judged to be 6 GB 2 190 020 A 6 .bad-- amount of inactive additional particles having va(8) lnttinsicviscositylnl, rious average particle diameters were added and, 19 of polyesterwas dissolved in 100 mi of a mixed 65 further, 0.04 part byweight of ethyl acid phosphate solvent of phenolitetracholorethane in a weight ratio and 0.04 part byweight of antimonytfioxidewere of 50: 50, and the intfinsicviscositywas measured at added to the reaction mixture and carried out 30-c. polycondensation for 4 hours, thereby obtaining a (9) Double refractive indexafterstretching in the polyethyleneterephthalate (polyester B) having an machine direction 7() intrinsic viscosity of 0.63.

The retardation was measured by a polarizing A predetermined higher aliphatic monecaTboxylic microscope produced by Carl-Zeiss Stiftung, and the acid sodium was dry blended with polyesterAand double refractive index (A n) was obtained from the polyester B by using a hiaxial extruderto obtain following formula. master batches having a high concentration.

(Lri) = Rfd 75 Materialsfor producing afilm havingdifferent mherein R represents retardation and dthethickness viscosities, contents of higher monocarboxylic: acid ofthefilm. sodium, kinds of particles, etc. were obtained by (10) Orientation ofbiaxiallyorientedfilm blending these polyesters A, polyesters Bandmaster The refractive indexes n.,, %and rip in three batches in appropriate ratios.

directions was respeetto the Na-D line was obtained 80 [Production of Film] at 25C by means of an Abbe refractometer produced Each of the abovedescribed materials of various byAtago Co., wherein n, isthe refractive index in the kinds was dried by an ordinary method, extruded at direction ofthickness, ny is that in the direction ofthe 2STC by an extruder, and was formed into an main orientation, and np isthat in the direction amorphous film by rapidly cooling by an electrostatic perpendicularto the main orientation. Fromthese 85 contactmethod.

values the degree of surface orientation (A p) was Thethus-obtained amorphousfilms were stretched obtained as---follows- in the machine direction in one stage ormuffiple stages to obtain films having various double refrac +n -U tive indexes (An). Thethus-obtained films were stretched by4t!mes by a tenter and were beat set at Examples 1 to 6andComparative Examples 1 to 4_ 230'C. Atthetime of heatsetting,theywere sub [Preparation of Polyester] jected to relaxation in the transverse direction by parts byweightof dimethyllerephthaUate,70 varying the relaxation ratio in the range of Oto parts byweightef ethylene glycol, 0.20 part byweight [Production of Magnetic Recording Medium] of lithium acetate dihydrate and 0.10 part byweightof Part by Weight calcium acetate monohydrate were charged into a Fewromagnetic powder (C- doped V-Fe20.5) reactor and heated to carry out esterexchange Cellulose acetate butygate reaction,whiie distilling off methanol. The reaction Epoxy resin temperaturewas gradually raised until thetempera- Silicon oil ture reached 23TCaftei---4 hourswhenthe ester Lecithin exchange reaction was substantially completed. Toluene (solvent) Thereafter, 0.23 part byweightoftriethyl phosphate Methyl ethyl ketone SolventD and 0-03 part byweightof phosphoric acid were Ethyl acetate (solventD addedtothe reaction mixture.

4() AfteraddingO.04partbyweightof antimony 95 Acomposition consisting ofthe above-desefibed trioxideto the mixture as a polycondensafion components was put into a hall mill andthoroughgy catalyst, polycondensation was carried out by an kneaded. 18,3 parts by weight of poly-osewganate ordinary method. More precisely, after antimony compound (Desmodur L-75D wans added thereto and trimoxidewas added, thetemperaturewas gradually the mixture was agitated for 30 minutes. The mixture raised and the pressure was gradually reduced, until 103 was applied to one side ofthe abzDvr,.-descfubsd thetemperature reached 2BO'Candthe pressure 15 polyef&- iV5eneterephthaUate film to a thickne-ss of 3pm - mmHg after 100 minutes- The pressure was further reduced unfit itfinally reached 0.3 mmHg. After a predeterminedfame, the pressure in the system was ums subjected to hardening treatment and pganEshEng E9 restored to ordinary pressure to obtain a 195 treatment, the film was sgitto a vi-adth of U2 inch to p,-,,,iyethyleneterephtbagate (polyesterAByvary-ing obtain a video taps.

the condensation time, pogeirsA having various The physical proper-fies and the characteristics of intrinsicviscosides were obtaine d. thethus-obtained oriented paUVesteirgUmsandthe Gntheotherhand, ICO parts byweightof dimethyd magnelfictapas obtained therefrom airesho%rm in E5 terephthalate,60 parts byweightof ethyleneggycoE 110 Table I.

and 0.09 part byweightof magnesiumacetate FromTablel, itiscUearthatthepngyeseirflUm tetrahydrate were charged into a reactorand heated havinga low surface woughne--.s according to the tlo carryout ester exchange reaction, while distilling present invention can he used asthe bass-55m fora uff methanol. The reaction temperature was gradualhigh-quaghf and high- densky recording medium C_U Ey raised until thelemparature reached 23TC after4 115 winhout a backcoat layer. Thus, a magnetic recording hours, when the ester exchange reaction was sub- medium according to the present invention has an stantially completed. Thereafter, an appropriate industrially high value- 7 GB 2 190 020 A 7 Composition (part by weight with respect Pile producing ditio.

to 100 parts by weight of polyester) Particles ffigher Aliphatic D-bl' K laxation rate Compound i.d. "' time () Inner Particles Small particles Large particles in th at of heat-setting Kind Amount machine direction A nt Ds (meter Kind Amount Kind Amount V.) Ex. 1 0.30 0.8 - - - - Comp d 0.20 0.105 0 (11) Ex. 2 0.30 0.8 - - - - C P d 0.20 0.105 0 (M) E 3 0.30 0.8 - - - - Compound 0.20 0.105 0 (1) Fx. 4 0.30 0.8 - - - - Comp)u 0.20 0.060 10 lo nd Synthetic synthetic Ex. 5 - - Calcium 0.40 Calcium 0.03 Compound 0.20 0.060 10 Carbonat Carb to (I) TOARd- 0.6 11 Synthetic Ex. 6 - - Oxide 0.40 Aum 0.03 Compound 0.20 0.060 10 "1b.n.t.

Car 0.30 u 0.6 p Synthetic E 7 Silica 0.40 C lb"u't. 0.0 C p u.d 0.20 0.060 in 3 Car (.) 0.40 U 0,6 p 1 0.30 0.8 0.105 0 C"PI . P. 2 0.30 0.8 10 Measured value and evaluation Oriented Polyester Film characteristics of magnetic tape D-ble De roe of p_ during i ""t' F Intrinsic an face A ""r Tra l- SC r viscosity tiv 5 orienta- (number/ r friction SO time fe' Adhesive iff 1 magnetic ghR th 1 conversion r', - ni, d tion 2 n tat repeated t tr nitgr. t in ex... e en a a An An sm (us'c travelling property E 1 0.58 0.006 1.6035 0.171 0 0.011 0.26 0.28 0.29 1,0 good 1 to 2 good E., 2 0.58 0.006 1.6035 0.171 0 0.011 0.24 0.26 0.27 1,0 good 1 to 2 good E 3 0.58 0.006 1.6035 0.171 0 0.011 0.22 0.24 0.25 @) m good 1 c. 2 good Ex. 4 0.58 0.015 1.6035 0.161 900 0.011 0.20 0.22 0.23 on 1.5 good 1 to 2 good E 5 0.58 0.015 1.6035 0.161 1200 0.011 0.20 0.21 0.21 1.5 ZZY, 1 good E.. 6 0.58 0.015 1.61035 0.161 700 0.011 0.20 0.21 0.21 1,5 very 1 good -.d Ex. 7 0.58 0.015 1.6035 0.161 2000 0.011 0.20 0.21 0.21 1.5 very 1 good good C P. d, not rur 1 0.58 0.006 1.6035 0.171 0 0.011 0.42 0.47 0.48 bad 3 us,, 1 ablc.s-- "' not 'u' 1.6033 0.161 900 0.011 0.32 0.40 0.42 bad 3 n..a InTable 1, compounds (1), (11) and (ill) havethe biaxial ly oriented polyesterfilm showing the average following structures. surface roughness Ra of 0.005to 0.013 pm, the static Compound (1) a mixture of compounds having the ' 25 cofficient (p.) of fifm-film friction of not morethan following formula: 0.28,the dynamic coefficient (11d) of film-film friction of not morethan 0.28, andthe maximum coefficient CH 3 -±CH 11---_---i- COONa of friction of not morethan 0.30 during 50- time CH 3 repeated travelling, said biaxially oriented polyester wherein 31-: n -539, and a melting point of 100 to 30 fi 1 m containing, with respect to 100 parts by weight of 11 01C polyester, Compound (11) a mixture of compounds having the (A) 0.001 to 1.0 part by weight of inner particles following formula: having an average diameter of 0.1 to 1.5 pm andlor inactive additional particles having an average dia CH 3-f-CH-2±,,-CII' COONa 35 meter of 0.1 to 1.0 pm and CH 3 (B) 0.005 to 2 parts by weight of an organic lubricantwhich comprises a mixture of higher wherein 15-: n:34, containing 30 wt% of the aliphatic monocarboxylic acids having respectively compounds in which 30:- n:-34, and having a melting different carbon numbers of not less than 18 andlor a point of 100 to 150T 40 mixture of derivatives thereof having respectively Compound (111) a mixture of compounds having the different carbon numbers of not lessthan 18, following formula: contains not less than 10 wt% of higher aliphatic CH3--CH2)-. COONa monocarboxylic acid(s) having not lessthan 34 carbon atoms and/or derivative(s) thereof having not CE3 45 less than 34 carbon atoms, and has a melting point of wherein 23:- n-: 39, containing 51 wt% of the 80 to 200T, compounds in which 30 -5 n:-:-2 39, and having a melting said higher aliphatic monocarboxylic acids and point of 100 to 130CC derivatives thereof being represented byformula (l):

Itisto be unde rstood that the present invention R also includesthe novel blaxially oriented polyester P film, which is suitable for use in preparing a magnetic R, - C - COOR 4 recording medium, as herein before described.

Claims (1)

1. CLAIMS wherein R, represents an alkyl group oran unsatu

   1. A magnetic recording medium comprising a 50 rated hydrocarbon group having not less than 10 R GB 2 190 020 A 8 carbon atoms, R2 represents an alkyl group having tivesthereof being represented byformula (l):

   not lessthan one carbon atom oran unsaturated R hydrocarbon group having notlessthan 2 carbon 12 atoms, R3 representsa hydrogen atom, an alkyl group PL, - C - COOR4 having notlessthan one carbon atom, oran unsaturated hydrocarbon group having not lessthan 2 carbon atoms, and R4 represents a hydrogen atom, wherein R, represents an alkyl group or an unsatu a metal, an alkyl group having not less than one rated hydrocarbon group having not less than 10 carbon atom oran unsaturated hydrocarbon group carbon atoms, R2 represents an alkyl group having having not lessthantwo carbon atoms,thetotal 70 not lessthan one carbon atom oran unsaturated numberof carbon atoms in R1,R2, R3 and R4being not hydrocarbon group having not lessthan 2 carbon lessthan 16; and atoms, R3 represents a hydrogen atom, an alkyl group a magnetic layer provided on one side of said having not less than one carbon atom, or an polyesterfilm. unsaturated hydrocarbon group having not less than 2. A magnetic recording medium according to 75 2 carbon atoms, and R4 represents a hydrogen atom, claim twherein said organic lubricant contains not a metal, an alkyl group having not less than one iessthan 20wt% of higher aliphatic monocarboxylic carbon atom or an unsaturated hydrocarbon group acid(s) having not lessthan 34carbon atoms andlor having not lessthan two carbon atoms, thetotal derivative(s) thereof having not lessthan 34 carbon number of carbon atoms in R,, R2, R3 and R4 being not atoms. 80 lessthan 16; 3. A magnetic recording medium according to melt extruding the mixture ata temperature of 250 claim 1 or claim 2, wherein said biaxial ly oriented to 31 OT into an amorphous film; polyester film satisfies the following relationships (2), stretching the amorphous film in the machine (3) and W: direction by 2.0 to 8.0 times at a temperature of 75 to 1.600-:55:- 1.606 (2) 85 1400C so thatthe double refractive index after A p:-: 1.43 H - 2.128 (3) stretching is 0.030 to 0.130; An _20 X 10-3 (4) stretching thethus obtained film in the transverse wherein 5 represents an average refractive index, A p direction by 2.0 to 5.0 times at a temperature of 90 to represents a degree of surface orientation, and A n 150oC; represents a double refractive index. 90 heatsetting thethus biaxially stretched film at a 4. A magnetic recording medium according to temperature of 200to 2400C for 1 to 60 seconds, anyone of the preceding claims wherein the number thereby obtaining a biaxially oriented polyester film Aof a pair of protuberances and depression, which is showing the average surface roughness Ra of 0.005 derived from said protuberances and has a major axis to 0.013 pm. the static coefficient (ps) of film-film of at least2 pm, perone mm2 of the surface of said 95 friction of not more than 0.28, the dynamic coefficient biaxial iy oriented polyester fi 1 m satisfies the fol [ow- (11d) of filmfilm friction of not morethan 0.28, and the ing relationship (5): maximum coefficient friction of not morethan 0.30 _ A (5). during 50-time repeated travelling; and 5. A magnetic recording medium according to forming a magnetic layer on one side of said any one of the preceding claims, wherein said 100 biaxially oriented polyesterfilm.

   biaxially oriented poiVesterfilm contains 0.1 to 1.0 7. A process as claimed in claim 6, wherein said part by weight of small-diameter inner particles organic lubricant contains not less than 20 wt% of having an average diameter of 0.1 to 0.6 pm and Oto higher aliphatic monocarboxylic acid(s) having not 0. 1 part by weight of large-diameter inactive addition- less than 34 carbon atoms andlor derivatives(s) al particles having an average diameter of 0.4to 1.0 105 thereof having not less than 34 carbon atoms.

   lim with respectto 100 parts by weight of polyester. 8. A process as claimed in claim 6 orclaim 7, 6. A process for producing a magnetic recording wherein said biaxialiy oriented polyester ffl m pro medium comprising the steps of duced by the process satisf ies the relationships (2), mixing a polyester polymer containing 0.001 to 1.0 (3) and W:

   part byweight of inner particles having an average 110 1.600;-15 111.606 (2) diameter of 0.1 to 1.5 lim andlor inactive additional Ap:-5 1.43 H 2. 128 (3) particles having an average diameter of 0.1 to 1.0 pm A n:-20 X 10-3 (4) with respeetto 100 parts byweight of polyester, with wherein H represents an average refractive index, A p 0.005to 2 parts byweight,with respectto 100 parts by represents a degree of surface orientation, and An weight of polyester, an organic lubricantwhich 115 represents a double refractive index.

   comprises a mixture of higher aliphatic monocar- 9. A process as claimed in any oneof claims 6to 8, boxylic acids having respectively different carbon wherein the resulting magnetic recording medium is numbers of not less than 18 andlor a mixture of such thatthe number A of a pair of protuberances and derivatives thereof having respectively different cardepression, which isderivedfrom said protuber bon numbersof notlessthan Mcontains notless 120 ancesand hasa majoraxis of atleast2 pm, perone than lOwt% of higheraliphatic monocarboxylic mm 2 ofthesurfaceof said biaxial ly oriented polyes acid(s) having notlessthan 34carbon atoms and/or terfilm satisfies the following relationship (5):

   derivative(s) thereof having notlessthan 34carbon 5:- A (5) atoms and has a melting point of 80 to 200T, said 10. A process as claimed in anyone of claims 6to higher aliphatic monocarboxylic acids and deriva- 125 9, wherein the resulting magnetic recording medium 9 GB 2 190 020 A 9 is such thatthe biaxially oriented polyesterfilm contains 0.1 to 1.0 part byweight of small-diameter inner particles having an average diameter of 0.1 to 0.6 pm and 0 to 0.1 part by weight of iarge-diameter inactive additional particles having an average diameter of 0.4to 1.0 pm with respectto 100 parts by weight of polyester.

   11. A process for producing a magnetic recording medium as claimed in claim 6 and substantially as hereinbefore described in anyone of the examples.

   12. A magnetic recording medium asclaimed in claim land as substantially described in anyone of the examples orwhen produced bythe process claim in any one of claims 6to 10.

   13. A biaxially oriented polyester film showing the average surface roughness Ra of 0.005 to 0.013 [im,the static coefficient (11s) of filmfilm friction of not more than 0.28, the dynamic coefficient (11d) Of film-film friction of not more than 0.28, and the maximum coefficient of friction of not more than 0.30 during 50-time repeated travelling, said biaxially oriented polyesterfilm containing, with respect to 100 parts byweightof polyester, (A) 0.001 to 1.0 part by weight of inner particles having an average diameter of 0.1 to 1.5 pm andlor inactive additional particles having an average diameter of 0. 1 to 1.0 lim and (B) 0.005 to 2 parts by weight of an organic lubricant which comprises a mixture of higher aliphatic monocarboxylic acids having respectively different carbon numbers of not less than 18 andlor a mixture of derivatives thereof having respectively different carbon n urn bers of not less than 18, contains not less than 10 wt% of higher aliphatic monocarboxylic acid(s) having not less than 34 carbon atoms andlorderivative(s) thereof having not less than 34 carbon atoms, and has a melting point of 80to 200T, said higher aliphatic monocarboxylic acids and derivatives thereof being represented by formula (l):

   R 12 R, C - COOR4 1 3 wherein R, represents an alkyl group oran unsaturated hydrocarbon group having not lessthan 10 carbon atoms, R2 represents an alkyl group having not lessthan one carbon atom or an unsaturated hydrocarbon group having not lessthan 2 carbon atoms, R3 represents a hydrogen atom, an alkyl group having not lessthan one carbon atom, or an unsaturated hydrocarbon group having not lessthan 2 carbon atoms, and R4 represents a hydrogen atom, a metal, an alkyl group having not lessthan one carbon atom or an unsaturated hydrocarbon group having not lessthan two carbon atoms, the total numberof carbon atoms in R,, R2, R3 and R4 being not lessthan 16.

   Printed in the United Kingdom for Her Majesty's Stationery Office by the Tweeddale Press Group, 8991685, 11187 18996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained.